Notes

Record Information

Source Institution:

University of Florida

Holding Location:

University of Florida

Rights Management:

The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.

Leptarctine remains have been reported from several
localities, of Miocene age, within the United States and in
only four instances has there been enough cranial material
preserved to warrant its published description (Dorr 1954,
1956; Gazin 1936; Stock 1930; Matthew 1924). This dearth
of crania is particularly true in the case of the animal from
the Florida Miocene, Leptarctus ancipidens, which hereto-
fore has been known only from partial upper dentitions, sup-
plemented by a lower jaw and several isolated molars and
premolars (Olsen 1957a,b; White 1941).

A nearly complete skull (fig. 1) of Leptarctus ancipidens
was recovered during the 1957 excavations at the Thomas
Farm by the Florida Geological Survey and is the basis for
this contribution to the cranial anatomy of this rare Tertiary
mustelid. The knowledge gained by the comparison of this
skull of the Thomas Farm species ancipidens(F. G. S. V-5706)
with those of other members of the genus Leptarctus has
further strengthened the writer's original opinion, based on
dentition alone, that this is indeed a species of Leptarctus
rather than representing a new genus of mustelids as de-
scribed by White (1941). The comparison of the monotypic
genus Mephititaxus, with the known Leptarctines, and its
reduction to the synonomy of the genus Leptarctus was dis-
cussed in an earlier contribution by thewriter (Olsen 1957b).

The types, with casts of the types or figured specimens
of the following species, have been at hand for comparison
or have been examined: Leptarctus primus Leidy, A. M. N. H.
18241; Hypsoparia bozemanensis Dorr, C.M. 9574; Cratero-
gale simus Gazin, U.S.N.M. 13801; Leptarctus ancipidens
(White), M.C.Z. 3658.

The most striking characters of the skull of L. ancipidens
are the double temporal ridges, the bony projections of the
bullae and the relatively slight rostrum as compared with the
thickened and rugose area that supported the craniomandib-
ular and neck musculature.

TemporalRidges: The temporal ridges originate at the
postorbital processes of the frontals and diverge backward
to merge with the lamboidal crests which curve downward
to terminate at the mastoid processes (fig. IB). Dual crests
of a similar nature, but not so proportionally massive as
those found in Leptarctus, are known to occur in the present
day genera ofTaxidea andMartes. This strong up-thrusting

SPECIAL PUBLICATION NO. 2 PAPER NO. 2 3

S~ "4

0I- y / ^oi il e ..-0

.XI \ | -- I
>- z5 rI .- ,1 In -i 0
S" -- 0
00 t0 0 A

.5 I- a .--x- ..< -' 0 M"
4 ) c.
0 44

I\ r- ." ' p .
00
o w

cd L

ta

FLORIDA GEOLOGICAL SURVEY

of the temporal crests indicates a hypertrophied muscula-
ture. This is particularly disturbing inasmuch as the teeth
and the mandibular articulations do not indicate an especially
powerful masticatory function for this animal.

Bullae: The bony projections that extend in an antero-
ventral direction from the bullae are, as far as is known,
found only in Leptarctine skulls (fig. lA, 2). Gazin (1936)
described their function as being an attachment for the di-
gastric muscle. In carnivores, the attachment of the digastric
muscle is typically associated with the paroccipitalprocess
and the ridge connecting this with the mastoid process (fig.
lA, C; 3). In Leptarctus ancipidens, this same attachment
site is marked by a scar plainly visible on the described
specimen.

The sole function of the digastric muscle is that of de-
pressing the lower jaw and opening the mouth. The muscle
performing this operation in the carnivores is composed of
1
two fusiform flattened bellies, united by a round tendon.
I do not believe that the digastricus, performing the slight
function that it does, would have need for such a rugose at-
tachment site as indicated by the bony process of the tym-
panic. Undescribed specimens of Leptarctus in the collection
of the Frick Laboratory at the American Museum of Natural
History, indicate that this process can vary in size and that
the foramen or aperture can be present or entirely lacking
(Frick, personal communication, October 1957). This open-
ing which is present in the Florida form and absent in some
specimens from other localities, may be due to the incom-
plete fusion of the twin inferiorly directedprocesses arising
from the auditory bullae. The muscles that are associated
with this area are those which depress the head at the atlanto-
occipital articulationbutwhether or not any of these muscles

1These bellies fuse in the dog and the hame digastricus
or "two-bellied" does not apply (Miller 1952, Sisson 1953).

SPECIAL PUBLICATION NO. 2 PAPER NO. 2 5

6 co

N a;

d 41

00

omm

0 0
< h

\~~~ a <

FLORIDA GEOLOGICAL SURVEY

were associatedwith this tympanic projection cannot be stated
with certainty.

The tympanic, although crushed in the figured specimen,
has enough of its internal structure preserved to warrant
a more detailed description (fig. 2). The tympanic cavity
does not extend into the twin lobes of the process but ends
short of the foramen or aperture that pierces the distal end
of the process. The two lobes consist of compact bone and
do not contain nutrient foramina. The interior of the tym-
panic cavity has two radiating septa, one arising from the
anteromedial wall of the cavity and ending at the wall of the
internal meatus and the other radiating from the lateral wall
of the tympanic and fusing with the more or less crescent
shaped crista tympanica.

There is considerable space between the crista tym-
panica and the ventral floor of the tympanic cavity; a similar
condition is found in the badger (Pocock 1921, Segall 1943).
The bulla of the badger is very similar to that of Leptarctus
having four additional septa or "rafters" plus the two found
in the Miocene form (Van der Klaauw 1931). The external
auditory meatus has no external ring or tube, being instead
an opening similar to those marking the entrance of the larger
bloodvessels having a rounded margin to the external open-
ing. The meatus enters the tympanic cavity at a nearly right
angle to the median sagittal plane.

Foramina: The external opening of the stylomastoid
foramen is located at the base of the mastoidprocess andits
course can be traced by a tube-like swelling visible on the
roof of the tympanic cavity to its terminus at the posterior
base of the crista tympanica. The area of the cavity above
this opening and that of the internal auditory meatus has been
destroyed by crushing so that it cannot be interpreted with
any degree of confidence.

The postglenoid foramen is located, as in the badger,
at the base of the postglenoid process. The foramen ovale

SPECIAL PUBLICATION NO. 2 PAPER NO. 2 7

is situated at the anterior base of the bullaand in a posterior
position in relation to the pterygoid process. The foramen
hypoglossihas its external opening at the posteromedial base
of the bulla, again similar to that found in the badger (fig.
1A, C).

The lacrimal duct and the infraorbital foramen are po-
sitioned as in the badger and there is a noticeable swelling
on the anterior margin of the lacrimal. This swelling is also
present in the types of Craterogale simus and Hypsoparia
bozemanensis.

Zygomatic Arch: The fact that the zygomatic archis
much heavier in proportion to the other dimensions of the
skull has been the cause of much discussion among the de-
scribers ofLeptarctine skulls. Dorr (1954) used this feature
as main distinction between his new genus Hypsoparia and
the other genera of Leptarctines. There are not enough
cranial remains known of Leptarctus to evaluate to what de-
gree these animals varied but that they did vary considerably
is brought out in the two lower jaws that are preserved, both
possessing Mi. In F.G.S. V-5655, the depth of ramus be-
low M- is 30 percent greater than the same measurement in
F. G. S V-5697. The anteroposterior diameter of M- is only
17 percent greater in the deeper jawed specimen. Consider-
able variation among badger skulls was noted by Hall (1946)
and applied to his study of the Pliocene form Pliotaxidea.
This variation also holds true for Leptarctines.

Hall (1951) figures a number of mustelid skulls in which
the width of the zygomatic arch varies considerably and yet
these specimens are of the same species, Mustela frenata
(pl. 32, 33; fig. a, d). The dentition of H. bozemanensis is
morphologically indistinguishable from other members of the
genus Leptarctus. The proportion of width versus length in
M- has already been discussed in a previous paper (Hall
1936, p. 61; Olsen 1957b, p. 4).

Validity of Hypsoparia: I believe that the allocation of
the species bozemanensis to a new genus Hypsoparia is not

FLORIDA GEOLOGICAL SURVEY

valid, when such an assignment is based ona variable char-
acter as a zygomatic arch, known in only one specimen. I
propose that the genus Hypsopariabe reduced to the synonymy
of the genus Leptarctus.

The rostrum is slight in build compared to the heavy
zygomatic arch, the temporal crests and the strong attach-
ment site for the digastric muscle. The sutures, bounding
the various elements making up the skull cannot be distin-
guished from the post-fossilization cracks so it is not pos-
sible to determine, with any degree of accuracy, which of
these elements have undergone the most change in regardto
growth or reduction.

Dentition: The dentition of L. ancipidens has the fol-
lowing formula: I-, Cl' P3, Mi. The teeth, with the ex-
ception of the incisors and canines, have been previously
figured and described (Olsen 1957a,b; White 1941). The
incisors and canines are lacking in the figured specimen but
their size and location are determined by the preserved al-
veoli as being quite similar to those of the living badgers.

The teeth of Craterogale do vary morphologically from
those of the genus Leptarctus. The hypocone of P is lack-
ing inCraterogale and although this same tooth varies some-
what inthe known species of Leptarctus, this cusp is always
present. The projection of the auditory bulla of Craterogale
also has more of a forward or anterior deflection than those
found in Leptarctus.

Just why an animal so similar to the present daybadger
would require as heavy an occipital musculature as postu-
lated by the muscle attachments and yet have a mandible of
"normal" badger proportions is a puzzling question that is
not answerable from the material now at hand.

SPECIAL PUBLICATION NO. 2 PAPER NO. 2 9

ACKNOWLEDGMENTS

Iwish to thank Dr. Childs Frick for information relating
to specimens of Leptarctus in the Frick collection at the
American Museum of Natural History, and Dr. C. L. Gazin
for permission to study the type of Craterogale which is in
the collection of the U. S. National Museum. Dr. D. Dwight
Davis of the Chicago Natural History Museum was particu-
larly helpful in relation to my inquiries regarding the otic
region of this mustelid. The accurate and detailed draw-
ings are the work of Mr. Andrew Janson, Scientific Artist
for the Florida Geological Survey. The credit for the dis-
covery of this fine specimen goes to Mr. J. William Yon,
Jr., Geologist with the Florida Geological Survey, without
whose careful excavation this singular skull would undoubt-
edly have been lost beyond recovery.

REFERENCES

Dorr, J.A.
1954

Hypsoparia bozemanensis; a new genus and
species of Leptarctine mustelid from the late
Miocene Madison Valley formation of Montana:
Annals of the Carnegie Mus. art. 9, vol. 33,
p. 179-184.